Hi kate,
Unfortunately it’s not possible to “diagnose” mattress comfort issues on a forum with any certainty because you are the only one that can feel what you feel on a mattress and there are too many unique unknowns, variables, and complexities involved that can affect how each person sleeps on a mattress (or a mattress/topper combination) in terms of “comfort” and PPP (Posture and alignment, Pressure relief, and your Personal preferences) or any “symptoms” they experience so a mattress and topper combination that may be “perfect” for one person may be completely unsuitable for someone else to sleep on.
Having said that … there is more about the most common symptoms that people may experience when they sleep on a mattress and the most likely (although not the only) reasons for them in post #2 here.
The most common (although not the only) reason for lower back pain is a mattress that is too soft (either the comfort layers are too thick/soft or the support core is too soft) so I would be cautious about adding any additional softness to a sleeping system that is already causing you lower back pain unless you are confident that what you are sleeping on is too firm.
Whether you use the latex on top or the memory foam on top would be strictly a preference choice depending on which combination your personal experience indicates you tend to prefer. Having the latex on top would probably be a little cooler for most people and would provide a more resilient sleeping surface that may be less “motion restricting” with some of the feeling of slowly sinking in to the memory foam underneath it and having the memory foam on top would give you more of a memory foam and slow response feel that transferred a little less motion with some of the additional “spring” and resilience of the latex underneath it but it would also depend on many other factors as well including the specific properties of the memory foam you are using (there are many different versions of memory foam with different properties) and the type and firmness of the latex as well because sleeping on thicker layers of soft foam of any type will “allow” you to sink in more which can be more insulating and can lead to temperature regulation issues for some people.
While it’s not possible to quantify the sleeping temperature of a mattress for any particular person with any real accuracy because there are so many variables involved including the type of mattress protector and the sheets and bedding that you use (which in many cases can have just as significant an effect on temperature as the type of foam in a mattress) and on where you are in the “oven to iceberg” range and because there is no standardized testing for temperature regulation with different combinations of materials … there is more about the many variables that can affect the sleeping temperature of a mattress or sleeping system in post #2 here that can help you choose the types of materials and components that are most likely to keep you in a comfortable temperature range. In very general terms … the layers and components of a sleeping system that are closer to your skin will have a bigger effect on airflow and temperature regulation than layers and components that are further away from your skin.
I don’t have any specific suggestions or recommendations because you are the only one that can feel what you feel on a mattress/topper combination and there are too many unknowns, variables, and personal preferences involved for anyone to be able to predict or make a specific suggestion about which topper would be the best “match” for both you and the mattress you are using it on in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) based on specs (either yours or a mattress) or “theory at a distance” that can possibly be more accurate than your own personal testing or sleeping experience (see mattress firmness/comfort levels in post #2 here). The specifics of the mattress under the topper can also make a significant difference in which topper will work best for any specific person since every layer and component in a mattress/topper combination will affect the feel and performance of every other layer and the “sleeping system” as a whole.
A topper can certainly be an effective way to add some additional softness, “comfort” and pressure relief to your sleeping system but adding a second topper only to improve temperature regulation (rather than using it to soften your mattress) would be more risky. The only way to know whether a specific topper in combination with your mattress and your current topper is a good “match” for you in terms of PPP would be based on your own careful testing or personal experience. If you can’t test the combination in person then there is always some risk and uncertainty involved in adding a topper because the specifics of the mattress itself and the topper you are already using along with your own body type, sleeping position, and preferences can affect which specific topper would be a suitable choice on any specific sleeping system.
While it’s not possible to make specific suggestions because of all the many variables involved that are unique to each person and your own experience is the only way to know for certain whether any mattress/topper combination will be a good “match” for you in terms of PPP … there is more information about choosing a topper in post #2 here and the topper guidelines it links to which along with a conversation with a reliable supplier that can provide you with good information about how their toppers compare to each other or to other toppers they are familiar with that are available on the market can help you use your sleeping experience on your current sleeping system as a reference point and guideline to help you choose “how much” additional softness you may need and the type, thickness, and firmness for a topper that has the least possible risk and the best chance for success. It also includes a link to a list of some of the better online sources for toppers I’m aware of as well.
When you are uncertain about which topper will work best with your mattress and you can’t test the combination in person then the return/exchange policy can be one of the most important parts of the “value” of a topper purchase just in case the topper you choose doesn’t work out as well as you hoped for.
If all else is equal … Talalay tends to be more breathable than Dunlop so there are some people that may notice some difference between them.
It’s impossible to know whether any combination of materials will lead to back pain but as I mentioned the most common cause for lower back pain is a sleeping system that has softer comfort layers that are too thick and/or soft or a support core that is too soft … regardless of the type of materials.
Memory foam and latex are very different materials with very different properties but the choice between them would be a preference choice not a “better/worse” choice. There is more about the pros and cons of memory foam vs latex in post #2 here.
The choice between Talalay and Dunlop is also a preference choice vs a “better/worse” choice and there is more about how they compare in very general terms in post #7 here.
Memory foam and latex will feel different regardless of their firmness level and the firmness of memory foam can also vary with temperature, humidity, and the length of time it is continuously compressed … to the degree that it’s possible to compare them at all then softer versions of latex (in the range of about 14 ILD - 19 ILD) would probably feel closer to memory foam than firmer versions of latex.
Phoenix